This invention relates to an improved, elongated, rod-like, rack used in automotive-type steering gear assemblies and similar types of mechanisms which utilize a pinion means for transmitting power through a rack and linkage to other elements. The improvement is concerned with lightening the weight of the rack and reducing the expense of its manufacture.
Automotive-type steering gear assemblies include an elongated rod which is engaged at one end by a pinion means for moving the rod, and is connected at its opposite end to elements for causing the wheels of the vehicle to turn. In essence, the rod consists of an elongated, steel bar having gear-like rack teeth machined, such as by broaching or machine tool cutting, transversely along one end portion thereof. The opposite end portion is typically provided with external threading for threadedly engaging with a coupling to another element. It is important that the rod-like rack be strong and rigid and, therefore, it is relatively heavy in weight.
Attempts have been made to reduce the weight of the rod-like rack by cutting away portions of the metal. That is, attempts have been made to reduce weight by drilling away the central portion of the link part of the rod, leaving the rack tooth bearing portion solid for strength purposes. However, in drilling the central portion of the rack part of the link of the rod or bar, the remaining wall must be left relatively thick in order to permit forming threads on its free portion. In addition, it is common to drill small openings through various portions of the rack for the passage of fluids therethrough.
The drilling away of portions of the rod or bar, in the vicinity of the link part of the rod, is relatively expensive and time consuming. Thus, there has been a need for some practical, inexpensive, method for producing rod-like racks with substantial hollow portions for lightening the weight of the part while, at the same time, not reducing the overall strength and rigidity of the part. The rack is made by means of a generally known cold forming extrusion process, but with certain improvements. The underlying prior art process is illustrated, for example, in my prior U.S. Pat. Nos. 3,837,205 issued Sept. 24, 1974 for a "Process for Cold Forming a Metal Tube with Inwardly Thickened End", 3,886,649 issued June 3, 1975 for a "Process for Cold Forming a Metal Tube with an Inwardly Thickened End", 4,277,969 issued July 14, 1981 for a "Method for Cold Forming Tubes Within Interior Thicker Wall Sections" and 4,292,831 issued Oct. 6, 1981 for a "Process for Extruding Metal Tube with Inwardly Thickened End Portions". This invention is concerned with providing an improved rack and method for forming the rack by cold extrusion.